New boiler help - how do I choose ?

MehulLakhani · 18 Nov 2018 at 20:04

Hi All

Our current boiler is dying slowly. BG Homecare have already made the trotters broom type joke. It is getting more and more unreliable. It is a 14 year old Baxi 100HE, condensing boiler.

The house is a 2004 built detached, with 5 beds, and 3 floors. 20 rads in total.

The Baxi is configured with a pump on top, to get the water around the system. It is a pressurised system with a cylinder upstairs in a cupboard, and the boiler is in the garage - so space is not a problem.

My trusted heating engineer has recommended a WB 30Ri, as he says that he wants to use an external pump, like I have at the moment, and the other WB boilers have a built in pump ?

The boiler does an okay job, but not great in terms of getting all the rads hot. So my thinking was a more powerful boiler and pump would help this ? I have had it flushed/balanced etc etc

What would the boiler guru's on the forum recommend ? The chap is happy to fit WB or Vailant. The other choice is a 40 CDI, or a vailant model of some sort.

Money is not my prime concern, but reliability is, and I need it powerful enough to get all the rads hot.

Any ideas gratefully appreciated .

R

Mehul

Sin_Chase · 18 Nov 2018 at 20:43

You need to work out how much demand your house generates first.

You don't want to grossly oversize your boiler, nor undersize.

Calculate your heating and water demand then size a boiler appropriately. Some let you set upper and lower outputs but you can still want to be in the right ballpark.

I might be wrong but I thought most modern condensing boilers are pressured now?

NickK · 18 Nov 2018 at 22:59

Sounds about right - our 32cdi shoves out 24kW for CH which is about 12 rads average.

The 30ri shoves out 30kW for CH. So 15 rads but if your house is 3 floors then it may need help pushing the weather up to the top floor.
The 32cdi has a pump but there’s a maximum head.

MehulLakhani · 18 Nov 2018 at 23:01

Thanks for all your replies.

We have 20 rads total. Some are quite small ones in bathrooms etc, but it is a fair amount of work for any boiler.

Would a 40CDI be a good option ? Does that have a pump built in ? I would rather go for a better "external one" - see below pic - we currently have a Grundfoss one.

|https://thumbsnap.com/mYppyrzG

|https://thumbsnap.com/GdgF3gWq

R

Mehul

RockLobster · 19 Nov 2018 at 11:15

This will give you an idea - https://www.worcester-bosch.co.uk/products/boilers/find-a-new-boiler/tool?user_type=homeowner

NickK · 19 Nov 2018 at 11:37

Just get a couple of quotes from plumbers - we had our entire system redone (old open system ripped out with boiler relocated). In the end I asked to up our boiler from a 28cdi to a 32cdi as the CH was the same but the HW was a over a litre/min more which works well with out mains pressure.

MehulLakhani · 19 Nov 2018 at 12:00

Hi All

My trusted engineers has come back to me with two options

Worcester greenstar 40 cdi classic regular

or

Vaillant 435

Which one should I plump for ?

Because of the way our house is built, the boiler will often need to run at a low level to keep the house warm. Which one can modulate lower ? Both of them are quite powerful, and I dont want to be burning gas when I dont need to.

R

Mehul

panthro · 19 Nov 2018 at 12:59

The rule of thumb is 1Kw per room (or per radiator if the room has multiple radiators) plus 10%. If you have 15 radiators in theory your boiler needs to be a minimum of 16.5Kw. I have 13 (I think) and have an Ideal Logic 18kW system boiler that works perfectly in a 4 bed detached 2 storey house. All rads are hot within a few minutes.

NickK · 19 Nov 2018 at 13:36

panthro said:
The rule of thumb is 1Kw per room (or per radiator if the room has multiple radiators) plus 10%. If you have 15 radiators in theory your boiler needs to be a minimum of 16.5Kw. I have 13 (I think) and have an Ideal Logic 18kW system boiler that works perfectly in a 4 bed detached 2 storey house. All rads are hot within a few minutes.

Size of efficiency of rads makes a difference too. One of ours kicks out 7000+ BTU (think that’s about 2kW) but your right in that it only needs that on the odd occasion (-17degC). We also have a large towel rail radiator (5K btu).

We have the Honeywell controller - not WiFi linked but radio linked and you can program temp over time. We then use TRVs to control the temp in each upstairs room. The boiler we have can set the CH water temp as well as the tap temp seperately.

I set the temp low during the day and only if we have a cold snap does it need to kick in. How that would work with 3 floors I don’t know. I assume the ground floor is the coldest and the upper floors are easier to control with TRVs to top up the rising heat?

Bosch now do a intelligent controller too with radiator linked control (£54 each!).